The separation of particulate matter from industrial fluid streams is often accomplished using laminate filters. These textile-based laminate filters remove particulates from the streams. When the resistance to flow or pressure drop through the textile caused by accumulation of particulate on the filter becomes significant, the filter must be cleaned, and the particulate removed from the filter.
It is common in the industrial filtration market to characterize the type of filter bag by the method of cleaning. The most common types, of cleaning techniques are reverse air, shaker, and pulse-jet. Reverse air and shaker techniques are considered low energy cleaning techniques.
In reverse air filtration techniques particulate collects on the interior of the bag. During cleanings, a gentle backwash of air collapses the bag and fractures the dust cake off the bag, which dust exits the bottom of the bag into a hopper.
Shaker mechanisms clean dust cakes that collect on the inside of a bag as well. The top of the bag is attached to an oscillating arm which creates a sinusoidal wave in the bag to dislodge the dust cake.
In Pulse-jet filtration, the particulate is captured on the outside of the bag. Pulse-jet cleaning techniques employ a short pulse of compressed air that enters the interior top portion of a filter bag or tube. The energy of this cleaning pulse expands the bag, knocking off the dust cake. The bag, will typically snap back to a cage support and go right back into service collecting particulate.
Of the three cleaning techniques, pulse-jet is the most stressful on the filter media. However, in recent years, industrial process engineers have increasingly selected pulse-jet baghouses for dust collection applications because of:    1. Smaller unit size (sometimes as much as ½ or ¼ the size of shakers and reverse air) due to:    (A) higher volumetric airflow/cloth area ratio (higher operating velocity through media); and    (B) on-line cleaning allows the unit to be designed at the desired flow rate, hence there is no need for additional filter media area to allow for off-line cleaning.    2. Minimal number of moving parts.    3. Lower number of bags to replace.
In a pulse-jet baghouse, bags are inserted into the baghouse with a metal cage on the inside to keep them from collapsing. Dirty air containing dust enters the baghouse on the outer side of the bag where the dust accumulates on the surface. The cleaned air travels through the bag and out of the baghouse. When a sufficient amount of dust has accumulated on the outside of the bag to cause a decreased amount of air flow through, the bag, the pulse-jet baghouse sends a pulse of high pressure air backwards through the bag. The accumulated dust is forced off the bag for collection in the lower portion of the baghouse by a combination of the high pressure air and the movement in the bag caused by the back pulse. This cleaning process may occur multiple times an hour to maintain sufficient air flow through the bag.
The movement in the bag mentioned above is a result of high pressure air imparting a stress on the bag. This imparted stress causes the bag to strain in all directions. When a seam is stressed, leak paths may develop which may expand over time, thus allowing dust to escape the baghouse. If stitch holes are present at a seam, when the seam is stressed, the stitch holes can also become leak paths which may expand over time, allowing dust to escape the baghouse. The seam itself may be strong enough to withstand stress without breaking; however, when a seam tape is applied to the seam to block the entry of dust into these leak paths, the seam tape should desirably remain substantially free of cracking, peeling or breaking under stress.
Any seam tape that is applied to the seam needs to survive repeated bag cleaning cycles (>50,000) during the life of the bag (>3 years).
However, currently available seam tapes used to seal the seam of a filter bag cannot withstand the repeated stresses of multiple pulse-jet cleaning cycles over the lifetime of the filter bag. Due to seam geometry and how the seam tape is applied to the seam, crosswise direction stresses concentrate within the seam tape. These stresses result in premature cracks and can expose stitch holes in the seam down the length of the filter bag. These cracks and holes are leak paths which may results in increased dust emissions.
Therefore, seam tapes used for sealing the seams of filter bags needed to withstand multiple cleaning cycles (>50,000) without substantially cracking or peeling, where cracking and peeling allows for particulate matter infiltration through the seam.
The EPA has passed new, more stringent regulations for both existing and new particulate matter sources in regard to further reducing particulate matter emissions from cement plants. To ensure compliance with the regulations, filter bag manufacturers need to: thus further reduce emissions from filter bags in the baghouse.
There therefore remains an unresolved need for seam-sealed filter bags and for seam tapes for sealing the seams of filter bags, which can withstand multiple pulse-jet or reverse-air cleaning cycles over the lifetime of the filter bag, and, advantageously limit particulate emissions to levels-which meet EPA standards.